Process for producing conductive rubber roller, and roller for electrophotographic apparatus

ABSTRACT

This invention provides a process for producing a conductive rubber roller having small aspect ratios of inner and outer diameters, having a stable measure of its inner diameter, having uniform cell distribution and being free from non-uniformity of hardness and electrical resistance in the peripheral direction. The process has a step of continuously extruding a tube composed of a specific unvulcanized rubber composition from a rubber extruder in a microwave vulcanizing unit, and a step of foaming and vulcanizing the tube by using a microwave irradiator having a microwave irradiation zone 4 m or less in length while being transported at given speed. The foamed rubber tube has an inner diameter 20 to 35% smaller than the outer diameter of the conductive core material over the whole region in the lengthwise direction, and the conductive core material is press-fitted into the foamed rubber tube without using any adhesive.

This application is a continuation of International Application No.PCT/JP2006/302912, filed Feb. 14, 2006, which claims the benefit ofJapanese Patent Application No. 2005-036079 filed Feb. 14, 2005,Japanese Patent Application No. 2005-036080 filed Feb. 14, 2005,Japanese Patent Application No. 2005-047222 filed Feb. 23, 2005,Japanese Patent Application No. 2005-049003 filed Feb. 24, 2005,Japanese Patent Application No. 2005-053816 filed Feb. 28, 2005, andJapanese Patent Application No. 2006-027022 filed Feb. 3, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for producing a conductive rubberroller used in image forming apparatus such as an electrophotographiccopying apparatus, a printer and an electrostatic recording apparatus,and also to a roller for electrophotographic apparatus, such as atransfer roller, set in an image forming apparatus in which atansferable image composed of a toner image is formed and held on animage bearing member such as a photosensitive member by an imaging meanssuch as an electrophotographic process or an electrostatic recordingprocess, and transferred to a transfer medium such as paper.

2. Related Background Art

Conductive rubber rollers such as a charging roller, a transfer rollerand a developing roller are used in many of imago forming apparatus ofan electrophotographic system, such as copying machines and printers. Toprovide these rollers with conductivity, a method is available in whicha conductive filler such a carbon black is added, or in which aconductive rubber material such as acrylonitrile-butadiene rubber orepichlorohydrin rubber is compounded. These roller are each kept incontact with a photosensitive drum under application of a load, and alsothese rollers are electrified for a long time on account of their use.Accordingly, it is desirable for them to be made of a rubber materialsmall in resistivity variation, and because of problems in productionprocesses, rubber materials such as acrylonitrile-butadiene rubber andepichlorohydrin rubber are widely used in the transfer roller and thecharging roller (see, e.g., Japanese Patent Applications Laid-open No.H10-171210 and No. 2002-070835).

The rubber material used for these rollers is kneaded together with avulcanizing agent, a blowing agent, a filler and so forth so as to bemade into a raw-material composition, which is then made into anunvulcanized, cylindrical rubber molded or extruded product by means ofa mold, an extruder or the like, and thereafter this molded or extrudedproduct is vulcanized and foamed by heating to make up a cylindricalfoam. Thereafter, a core material is press-fitted to the cylindricalfoam and then the peripheral surface of the foam is ground to have theshape of a roller. Such a method is used.

As methods for producing these conductive rubber rollers, the followingare conventionally available: vulcanization by means of a vulcanizerusing a high-pressure steam (see, e.g., Japanese Patent ApplicationLaid-open No. H11-114978), mold vulcanization carried out using acylindrical mold (see, e.g., Japanese Patent Application Laid-open No.H11-201140), and UHF vulcanization carried out by microwave irradiation(see, e.g., Japanese Patent Application Laid-open No. 2002-221859). Inthese methods, e.g., in the method of carrying out vulcanization bymeans of a vulcanizer, the cells in the roller foam obtained are sonon-uniform that grinding must be carried out in a large quantity inorder to expose the desired cells to the surface. In the moldingvulcanization carried out using a cylindrical mold, it takes time tomake preparations therefor, besides mold cleaning must be carried out.Hence, it has been unsuitable for producing rollers in a large number.

Firstly, although the method making use of UHF vulcanization can beeasily prepared and provides uniform cells, the tube formed may collapsewhen the rubber is softened, resulting in non-uniform aspect ratios oftube inner and outer diameters. This non-uniformity of the tube hascreated the non-uniformity of hardness and electrical resistance in theperipheral direction. In order to eliminate this non-uniformity of thetube, a method is known in which short UHF units are connected so as toslope the output of microwave irradiation. However, this method requiresa long and large apparatus and takes a long time to excessivelyirradiate the tube with microwaves, whereby the properties of the rubbermaterials, epichlorohydrin rubber and acrylonitrile-butadiene rubber,are changed, resulting the high volume resistivity of the rubbermaterial. Hence, the above method has been unsuitable for the conductiverubber rollers used in copying machines, printers and the like, and alsothere has been no presentation for any technical development directed tosmall-diameter rollers whose properties such as resistivity are requiredto delicately adjusted. To this vulcanized rubber tube, a conductivecore material coated at its preset position with a conductive adhesiveis press-fitted, followed by heat treatment, where the rubber tube maypartially come off because of non-uniformity of the adhesive, therebyresulting in non-uniform charging. Further, taking into account handlingof an organic solvent contained in the adhesive and environmentalproblems, it is desired to combine the vulcanized rubber tube and theconductive core material together without using any adhesive. It ispossible to fasten the vulcanized rubber tube to the conductive corematerial at a certain pressure, to thereby combine them together withoutusing any adhesive. However, in conventional techniques, the dimensionalstability of inner diameter is insufficient so that further improvementin precision has been sought for products. Because of such a background,in the production of conductive rubber rollers used in copying machines,printers and so forth, required to be free from the non-uniformity ofhardness and electrical resistance in the peripheral direction, it issought to provide a production process which is easily prepared forproduction steps and has good productivity.

Secondly, although the UHF vulcanization can be easily prepared andprovides uniform cells, the rubber softens to come to have a larger areain contact with a conveyor and a roller when the rubber tube is heatedin a furnace, thereby creating local non-uniformity in foaming.Especially where the rubber softens greatly, the rubber tube deforms tochange in its inner diameter, resulting in a poor yield of the rubbertube to bring about an economical problem. Further, the foamingnon-uniformity occurring in the rubber tube has been the cause of thenon-uniformity of hardness and electrical resistance in the peripheraldirection (see Japanese Patent Application Laid-open No. 2002-221859).Meanwhile, it is reported that a rubber tube having a double-layerstructure is used and an inner-layer rubber composition is selectivelyvulcanized to retain the inner diameter of the tube (see Japanese PatentApplication Laid-open No. 2003-246485). However, this has not remediedthe foaming non-uniformity. In all the cases presented above, nosufficient analysis is made in regard to the foaming non-uniformity, andhence the methods are insufficient for producing a roller having uniformcells.

Thirdly, although the UHF vulcanization can be easily prepared and alsoprovides uniform cells, the rubber softens to come to have a larger areain contact with a conveyor and a roller when the rubber tube is heatedin a furnace, thereby creating local non-uniformity in foaming.Especially where the rubber softens greatly, the rubber tube deforms tochange in its inner diameter, resulting in a poor yield of the rubbertube to bring about an economical problem. Further, the foamingnon-uniformity occurring in the rubber tube has been the cause of thenon-uniformity of hardness and electrical resistance in the peripheraldirection (see Japanese Patent Application Laid-open No. 2002-221859).In all the cases presented as above, no sufficient analysis is made inregard to the foaming non-uniformity, and hence the methods areinsufficient for producing a roller having uniform cells.

Where the above rubber material is heated with microwaves, the heatinglevel for the rubber can be controlled by changing a coefficient ofdielectric loss expressed by the product εr·tan δ of dielectric constant(εr) by dielectric power factor (tan δ). Taking note of this coefficientof dielectric loss, a method is reported in which the vulcanization iscarried out in the state that conductive carbon black is added andcompounded to a rubber component having a small coefficient ofdielectric loss (see Japanese Patent Applications Laid-open No.H06-344510 and No. H10-309725). In this case, a technique is employed inwhich a coefficient of dielectric loss is made as large as 1.0 in orderto heat a non-polar natural rubber. However, in a system containing apolar rubber as specified in the present invention, when a coefficientof dielectric loss is increased to be as large as 1.0, the rubber isoverheated in some cases.

Fourthly, although the UHF vulcanization can be easily prepared and alsoprovides uniform cells, the rubber softens to come to have a larger areain contact with a conveyor or a roller when the rubber tube is heated ina furnace. Especially in the initial stage of the vulcanization, theviscosity of the rubber decreases so greatly as to bring about such aproblem that the rubber tube adheres to the conveyor and roller and,especially in the case of the roller, it winds around the roller. Thishas caused a lowering of the yield in the vulcanization step and adecrease in the operation rate, to bring about an economical problem.Further, the foaming non-uniformity may occur at the contact surfacebetween the rubber tube and the conveyor or roller. This has been thecause of non-uniform hardness and electrical resistance in theperipheral direction. Also, in the cylindrical grinding for imparting aroller shape, the grinding is carried out in a large quantity in ordernot to leave non-uniformly ground portions, so that the rubber materialmust be discarded in a large quantity, bringing about an economicalproblem and an environmental problem as well (see, e.g., Japanese PatentApplication Laid-open No. 2002-221859).

Fifthly, in order to provide these rubber rollers with conductivity, thefollowing methods are conventionally available: a method in which aconductive filler such as carbon black is added and a method in whichepichlorohydrin rubber is mixed in acrylonitrile-butadiene rubber toreduce the resistivity in virtue of the epichlorohydrin rubber. However,a problem is raised in that the mixing of epichlorohydrin rubber in alarge quantity results in great variations in resistivity due to achange in environment such as temperature and humidity. Further, it isknown that, if a mixture with a large quantity of epichlorohydrin rubbermixed therein is irradiated with microwaves, the backbone chain etherlinkages are broken and the rubber may come to soften and deteriorate,resulting in unstable hardness of the roller. From such a background, inthe production of conductive rubber rollers used in copying machines,printers and so forth, for which it is required that cells in the foamedrubber layer are uniform, there is no non-uniformity of hardness andelectrical resistance in the peripheral direction, variations inresistivity in low-resistance ranges because of a change in environmentsuch as temperature and humidity are small and the hardness is stable,it is sought to provide a production process which is easily preparedfor production steps and good in productivity.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a process forproducing a conductive rubber roller for electrophotographic apparatus,such as a transfer roller, a charging roller or a developing roller,having a foamed rubber layer, obtained by heating a rubber compositiontube by irradiation with microwaves to foam and vulcanize it, havingsmall aspect ratios of tube inner and outer diameters, having a stablemeasure of its inner diameter, having uniform cell distribution, andbeing free from the non-uniformity of hardness and electrical resistancein the peripheral direction; and a roller for electrophotographicapparatus.

A second object of the present invention is to provide a process forproducing a conductive rubber roller used in image forming apparatus,having uniform cell distribution and being free from the non-uniformityof hardness and electrical resistance, a conductive rubber rollerobtained by such a production process, and a transfer roller as a typeof use of the rubber roller.

A third object of the present invention is to solve the problemsdiscussed above, to provide a conductive rubber roller used in imageforming apparatus, having uniform cell distribution and being free fromnon-uniform hardness, to provide a process for producing such aconductive rubber roller and to provide a transfer roller as a type ofuse of the rubber roller.

A fourth object of the present invention is to provide a process forproducing a conductive rubber roller used in electrophotographicapparatus, having uniform cell distribution, being free from non-uniformhardness and electrical resistance and brought to wear at a minimumlevel, and to provide a conductive rubber roller as a resultant productof the process and a transfer roller as a type of use of the rubberroller.

A fifth object of the present invention is to provide a process forproducing a conductive rubber roller for electrophotographic apparatus,such as a transfer roller, a charging roller or a developing roller,having a foamed rubber layer, obtained by heating an unvulcanized rubbercomposition tube by irradiation with microwaves to foam and vulcanizeit, having small aspect ratios of tube inner and outer diameters, havinguniform cell distribution, being free from the non-uniformity ofhardness and electrical resistance in the peripheral direction, beingsmall in resistivity variation due to a change in environment such astemperature and humidity, and having stable hardness; and to provide aroller for electrophotographic apparatus, and a transfer roller.

The invention for achieving the above first object (hereinafter referredto as the “first-object invention”) is a process for producing aconductive rubber roller having a conductive core material and a foamedrubber lay provided thereon, wherein

the foamed rubber layer is formed from a rubber composition containingepichlorohydrin rubber, acrylonitrile-butadiene rubber, an ethyleneoxide-propylene oxide-allyl glycidyl ether terpolymer, or a mixture ofany of these;

the process has an extrusion step of continuously extruding a tubecomposed of the rubber composition standing unvulcanized from a rubberextruder in a microwave vulcanizing unit, and a forming step of foamingand vulcanizing said tube by means of a microwave irradiator having amicrowave irradiation zone of 4 m or less in length while beingtransported at a speed of from 0.5 to 3.0 m/min to form a foamed rubbertube; and

the foamed rubber tube has an inner diameter smaller by from 20 to 35%than the outer diameter of the conductive core material over the wholeregion in the lengthwise direction of the conductive rubber roller, andthe conductive core material is press-fitted into the foamed rubber tubewithout using any adhesive. The first-object invention is also a rollerfor electrophotographic apparatus, characterized in that the conductiverubber roller produced by the above conductive rubber roller productionprocess of the present invention is used as a base layer member.

The invention for achieving the above second object (hereinafterreferred to as the “second-object invention”) is a process for producinga conductive rubber roller having a conductive core material and arubber layer provided thereon;

the rubber layer containing at least acrylonitrile rubber,epichlorohydrin rubber and a blowing agent;

the rubber layer having a gas generation rate of from 2 ml/g·min to 4ml/g·min at 170° C. to 230° C.; and

the process having a vulcanizing and foaming step of vulcanizing andfoaming the rubber layer by means of a microwave vulcanizing furnacewhich generates hot air and microwaves, where the temperature of theheating atmosphere in the microwave vulcanizing furnace in thevulcanizing and foaming step is so controlled that the ratio of initialvulcanizing time T10 to initial foaming time Tp10, T10/Tp10, of therubber layer is from 1 or more to less than 3 and the T10 is within 90seconds. In addition, the second-object invention is directed to the useof the above conductive rubber roller as a transfer roller set in atransfer mean of an image forming apparatus having an electrostaticphotosensitive member, a charging means, an exposure means, a developingmeans and a transfer means.

The invention for achieving the above third object (hereinafter referredto as the “third-object invention”) is a process for producing aconductive rubber roller having a conductive core material and a rubberlayer provided thereon;

the rubber layer containing at least acrylonitrile rubber,epichlorohydrin rubber and carbon black; and

the process having a kneading step of kneading the acrylonitrile rubber,the epichlorohydrin rubber and the carbon black in such a manner thatthe carbon black is in a content of from 5 to 30 parts by mass based on100 parts by mass of the total of the rubbers, and a vulcanizing andfoaming step of vulcanizing and foaming the rubber layer by means of amicrowave vulcanizing furnace which generates hot air and microwaves of2,450±50 MHz, where a dielectric loss coefficient εr·tan δ ofunvulcanized rubber through the kneading step is from 0.3 to 0.5. Inaddition, the third-object invention is directed to the use of the aboveconductive rubber roller as a transfer roller set in a transfer mean ofan image forming apparatus having an electrostatic photosensitivemember, a charging means, an exposure means, the developing means and atransfer means.

The invention for achieving the above fourth object (hereinafterreferred to as the “fourth-object invention”) is a process for producinga conductive rubber roller having a conductive core material and afoamed rubber layer provided thereon, wherein

the foamed rubber layer is formed through a step of carrying outvulcanization and foaming by irradiation with microwaves and hot air ina microwave vulcanizing furnace which carries out irradiation withmicrowaves;

a transport means in the microwave vulcanizing furnace is a mesh beltcoated with polytetrafluoroethylene; and

the ratio of an outer diameter A (mm) of the rubber layer after thevulcanization to a mesh opening percentage B (%) of the mesh belt, A/B,is from 0.2 or more to 0.4 or less. The fourth-object invention is alsoa conductive rubber roller used in electrophotographic apparatus, whichis produced by the above conductive rubber roller production process,and has a difference in Asker-C hardness of 1° or less in the peripheraldirection. In addition, the fourth-object invention is directed to theuse of the above conductive rubber roller as a transfer roller set in atransfer assembly of an electrophotographic apparatus.

The invention for achieving the above fifth object (hereinafter referredto as the “fifth-object invention”) is a process for producing aconductive rubber roller having a conductive core material and a foamedrubber layer provided thereon, wherein;

the foamed rubber layer is formed from a rubber composition containingfrom 0.1 to 50.0 parts by mass, based on 100 parts by mass of the totalpolymer content, of an ethylene oxide-propylene oxide-allyl glycidylether terpolymer having the propylene oxide in a compositionalproportion of from 1 to 20 mol % and the allyl glycidyl ether in acompositional proportion of from 5 to 15 mol %; and

the process has an extrusion step of continuously extruding a tubecomposed of the rubber composition standing unvulcanized from a rubberextruder in a microwave vulcanizing unit having an output of from 0.1 to1.5 kW, and a forming step of foaming and vulcanizing said tube by meansof a microwave irradiator having a microwave irradiation zone of 4 m orless in length while being transported at a speed of from 0.5 to 3.0m/min to form a foamed rubber tube. The fifth-object invention is alsodirected to a roller for electrophotographic apparatus, in particular, atransfer roller, characterized in that the conductive rubber rollerproduced by the above conductive rubber roller production process of thepresent invention is used as a base layer member.

According to the conductive rubber roller production process thefirst-object invention, a conductive rubber roller can be provided whichhas a foamed rubber tube having small aspect ratios of inner and outerdiameters of the foamed rubber tube, having uniform cell distributionand also being free from the non-uniformity of hardness and electricalresistance in the peripheral direction. In addition, a roller using as abase layer member the conductive rubber roller produced by the aboveconductive rubber roller production process can preferably be used asthe roller for electrophotographic apparatus, in particular, as thetransfer roller.

According to the conductive rubber roller production process of thesecond-object invention, the non-uniformity of foaming in the peripheraldirection does not come about, and hence a conductive rubber roller canbe provided which has uniform resistivity and hardness over the wholeroller region.

According to the conductive rubber roller production process of thethird-object invention, a conductive rubber roller can be provided whichhas, in particular, no cell non-uniformity especially in the peripheraldirection, and is free from hardness non-uniformity.

According to the conductive rubber roller production process of thefourth-object invention, the contact area between the rubber layerbefore vulcanization and foaming and the transporting mesh belt isoptimized to bring about no foaming non-uniformity, and hence aconductive rubber roller can be provided which has uniform resistivityand hardness over the whole roller region. Besides, since no foamingnon-uniformity may come about, grinding may be carried out in a minimumquantity, thus an economically and environmentally favorable productionprocess is provided.

According to the conductive rubber roller production process of thefifth-object invention, a conductive rubber roller can be provided whichhas a foamed rubber layer having uniform cells, is free from thenon-uniformity of hardness and electrical resistance in the peripheraldirection, and is small in variation in resistivity in low-resistanceranges because of a change in environmental such as temperature andhumidity, and has stable hardness. Also, a roller using as a base layermember the conductive rubber roller produced by the above conductiverubber roller production process can preferably be used as the rollerfor electrophotographic apparatus, in particular, as the transferroller.

Thus, the conductive rubber rollers produced by the above productionprocesses can preferably be used as rollers for electrophotographicapparatus, in particular, as transfer rollers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conductive rubber roller according toan embodiment obtained in the present invention.

FIG. 2 is a sectional schematic view of an image forming apparatushaving the conductive rubber roller, or the roller forelectrophotographic apparatus, of the present invention.

FIG. 3 is a sectional schematic view of an example of a vulcanizingforming system used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described below in detail.

(Description of Relationship between Conductive Rubber Roller of thePresent Invention and Image Forming Apparatus)

An example of an image forming apparatus having the conductive rubberroller, or the roller for electrophotographic apparatus, of the presentinvention, is shown in FIG. 2. The image forming apparatus shown in FIG.2 is a laser printer using a process cartridge, which is of anelectrophotographic system. FIG. 2 is a vertical sectional view showingthe outline of the construction of the laser printer. Also, in the imageforming apparatus shown in FIG. 2, the conductive rubber roller or theroller for electrophotographic apparatus obtained in the presentinvention is used as a charging roller 2, a transfer roller 6 or adeveloping roller 30.

The image forming apparatus shown in FIG. 2 has a drum typeelectrophotographic photosensitive member (which is referred to also asa photosensitive drum) 1 as an image bearing member. The photosensitivedrum 1 is one in which the periphery of a cylindrical aluminum supportis provided with a photosensitive layer formed of an organicphotoconductor (which is referred to also as an OPC). Thisphotosensitive drum 1 is rotatively driven in the direction of an arrowR1 at a stated process speed (peripheral speed) of, e.g., 50 mm/s by adrive means (not shown).

The photosensitive drum 1 surface is uniformly charged by means of acharging roller 2 as a contact charging member. The charging roller 2 isdisposed in contact with the photosensitive drum 1 surface, and isrotated in the direction of an arrow R2 as the photosensitive drum 1 isrotated in the direction of the arrow R1. To the charging roller 2, anoscillating voltage (alternating-current voltage VAC+direct-currentvoltage VDC) is applied from a charging bias applying power source (ahigh-voltage power source), whereby the photosensitive drum 1 surface isuniformly charged to −600 V (dark-area potential Vd). The photosensitivedrum 1 surface thus charged is subjected to scanning exposure to laserlight 3 emitted from a laser scanner and reflected from a mirror, i.e.,laser light modulated according to time-sequential electrical digitalimage signals of the intended image information. Thus, electrostaticlatent images (light-area potential V1: −150 V) corresponding to theintended image information are formed on the photosensitive drum 1surface.

The electrostatic latent images are reverse-developed as toner imageswith a toner 5 charged negatively and adhered to the photosensitive drum1 surface by the aid of a developing bias applied to a developing roller30 of a developing assembly 4.

Meanwhile, a transfer medium 7 such as paper, fed and transported from apaper feed section (no shown), is guided by a transfer guide, and is fedto a transfer zone (transfer nip zone) T formed between thephotosensitive drum 1 and the transfer roller 6, in such a manner as tobe synchronized with the toner images held on the photosensitive drum 1.To the surface of the transfer medium 7 fed to the transfer zone T, thetoner images held on the photosensitive drum 1 are transferred by theaid of a transfer bias applied to the transfer roller 6 from a transferbias applying power source (not shown). Here, toner (residual toner)remaining on the photosensitive drum 1 surface without being transferredto the transfer medium 7 is removed by means of a cleaning blade 8 of acleaning assembly 9.

The transfer medium 7 having passed through the transfer zone T isseparated from the photosensitive drum 1 and led into a fixing assembly10, where the toner images are fixed, and then put out of the imageforming apparatus main body as an image formed matter (a print).

(Description Concerning Conductive Rubber Roller Production Process)

A conductive rubber roller according to an embodiment, obtained in thepresent invention, is shown in FIG. 1 as a perspective view.

The conductive rubber roller of the present invention has a conductivecore material 61 and a foamed rubber layer 62 provided thereon. As theconductive core material 61, a round rod of a metallic material such asiron, copper or stainless steel may be used, which may preferably havean outer diameter of from 4 to 10 mm. The surface of such a rod mayfurther be treated by plating, for the purposes of preventing rust andproviding resistance to scratching.

In particular, the rubber composition which is a raw material forforming the foamed rubber layer 62 in the first-object inventioncontains epichlorohydrin rubber, acrylonitrile-butadiene rubber, anethylene oxide-propylene oxide-allyl glycidyl ether terpolymer, or amixture of any of these. If necessary, it further contains a blowingagent of an azodicarbonamide type; a vulcanizing agent such as sulfur,an organic peroxide, triazine or polyamine; a vulcanization acceleratorof a thiuram type, a thiazole type, a guanidine type, a sulfenic amidetype, a dithiocarbamate type or a thiourea type; a conducting agent suchas carbon black; a filler such as calcium carbonate; and otherauxiliaries. As the epichlorohydrin rubber, it is preferable to use,e.g., GECHRON 3106 (trade name), available from Nippon Zeon Co., Ltd.;as the acrylonitrile-butadiene rubber, e.g., DN 401 (trade name),available from Nippon Zeon Co., Ltd.; as the ethylene oxide-propyleneoxide-allyl glycidyl ether terpolymer, e.g., ZEOSPAN 8030 (trade name),available from Nippon Zeon Co.; and, as the blowing agent of anazodicarbonamide type, e.g., VINYFOR AC (trade name), available fromEiwa Chemical Ind. Co., Ltd.

In particular, the raw-material rubber used in the second- tofourth-object inventions includes acrylonitrile-butadiene rubber,epichlorohydrin rubber or a mixture of these as a rubber chiefcomponent, which is mixed in a stated quantity. Besides, it is possibleto use polymeric materials such as a polystyrene type polymericmaterial, a polyolefin type polymeric material, a polyester typepolymeric material, a polyurethane type polymeric material, a polyvinylchloride (PVC) or like thermoplastic elastomers, an acrylic resin, astyrene-vinyl acetate copolymer and a butadiene-acrylonitrile copolymer,and a mixture of any of these rubbers, elastomers or resins.

In the second- to fourth-object inventions, it is also possible to use aconducting agent such as carbon black, a filler such as calciumcarbonate, and a material known as a conductive substance added in orderto provide the rubber with conductivity. The conductive substance mayinclude conductive particles and an ionic conducting agent. For example,the conductive particles may include conductive carbon black, metaloxides such as TiO₂, SnO₂, ZnO and a solid solution of SnO₂ and SbO₃,and powder of metal such as Cu and Ag. The ionic conducting agent mayinclude LiClO₄ and NaSCN. Any of these may be added to and dispersed inthe rubber singly or in combination, whereby the desired electricalresistance can be achieved. The rubber may be made conductive byintroducing in the side chain or rubber backbone chain a molecule or thelike having a polarity.

In the third-object invention, the carbon black is in a content of from5 to 30 parts by mass based on 100 parts by mass of the total of therubbers. If the content is less than 5 parts by mass, when the rubbersare irradiated with microwaves, the heat value of the rubbers may beinsufficient to make the subsequent foaming reaction and vulcanizationreaction incomplete. If, on the other hand, the content is more than 30parts by mass, the heat value of the rubbers may be large, but where thecarbon black is poorly dispersed, non-uniformity of heating may occur orthe rubbers are excessively heated to undergo heat deterioration. Inaddition, there are no particular limitations concerning the type of thecarbon black. One having an average particle diameter of from 70 to 100nanometers may preferably be used.

As the blowing agent also used in the second- to fourth-objectinventions, an ADCA (azodicarbonamide) type agent is particularlypreferred. As other organic blowing agents, a DPT(dinitrosopentamethylenetetramine) type agent, a THS (p-toluenesulfonylhydrazide type agent, an OBSH (oxybisbenzenesulfenyl hydrazide) typeagent and the like may be used alone or in the form of a mixture. Thedecomposition temperature of the blowing agent may be lowered by adding,e.g., a blowing auxiliary agent such as urea resin or zinc oxide. Theblowing agent used in the present invention has been controlled to be soformulated that, in the rubber formulation specified in the presentinvention, the gas generation rate at 170° C. to 230° C. is from 2ml/g·min to 4 ml/g·min.

The blowing auxiliary agent used in the second- to fourth-objectinventions may include urea type compounds, metal oxides such as zincoxide and lead oxide, and compounds composed chiefly of salicylic acid,stearic acid or the like. A blowing auxiliary agent may be added whichcan be expected to appropriately act in conformity with the blowingagent used.

A vulcanizing agent used in the second- to fourth-object inventions mayinclude sulfur and metal oxides. Various vulcanization accelerators areknown. A thiazole type accelerator and a thiuram type accelerator may beused. The use of the thiazole type accelerator and the thiuram typeaccelerator in combination is commonly known to be effective in theexpression of properties against the deformation of rubber due tocompression (compression set). As a specific thiazole type accelerator,2-mercaptobenzothiazole and dibenzothiazyl disulfide are available. Inthe present invention, the dibenzothiazyl disulfide is preferred asbeing less in scorch properties involved with storage stability ofunvulcanized materials and being usable in combination with the thiuramtype accelerator. The thiuram type accelerator may includetetramethylthiuram monosulfide, tetraethylthiuram disulfide,tetrakis(2-ethylhexyl)thiuram disulfide, and dipentamethylenethiuramtetrasulfide. The tetrakis(2-ethylhexyl)thiuram disulfide is preferredas having superior anti-scorch properties. In addition, as to otherthiazole type accelerators and thiuram accelerators as well, they areusable in the present invention as long as their use conditions areadjusted.

In particular, as the thiuram type accelerator in the second-objectinvention, it is preferable to use one having a molecular weight of from200 or more to 650 or less. In virtue of its use, the balance betweenthe initial vulcanizing time T10 and the initial foaming time Tp10 iscontrolled. If it has a molecular weight of less than 200, thevulcanization rate may come so high as to make it difficult to effectsufficient foaming in the microwave vulcanization. If, on the otherhand, it has a molecular weight of more than 650, problems are liable tobe raised in that the cross-link density may be reduced so as for foamcells to become large, not only resulting in low hardness, but alsobringing about white lines on images because of the compression set ofthe roller.

In particular, the rubber composition which is a raw material forforming the foamed rubber layer 62 in the fifth-object inventioncontains 0.1 to 50.0 parts by mass, based on 100 parts by mass of thewhole polymer content, of a terpolymer composed of ethylene oxide,propylene oxide and allyl glycidyl ether, in which the propylene oxideis in a compositional proportion of from 1 to 20 mol % and the allylglycidyl ether is in a compositional proportion of from 5 to 15 mol %.As other polymer contents, the following may be contained:epichlorohydrin rubber, acrylonitrile-butadiene rubber, EPDM, butadienerubber, styrene-butadiene rubber, isoprene rubber, butyl rubber andchloroprene rubber, or a mixture of any of these. If necessary, thefollowing may be further contained: a blowing agent of anazodicarbonamide type; a vulcanizing agent such, as sulfur, an organicperoxide, triazine or polyamine; a vulcanization accelerator of athiuram type, a thiazole type, a guanidine type, a sulfenamide type, adithiocarbamate type or a thiourea type; a reinforcing agent such ascarbon black; a filler such as calcium carbonate; and other auxiliaries.As the ethylene oxide-propylene oxide-allyl glycidyl ether terpolymer,it is preferable to use, e.g., one having the ethylene oxide, thepropylene oxide and the allyl glycidyl ether in compositionalproportions of from 86.0 to 88.0 mol %, from 1.2 to 1.4 mol % and from11.0 to 13.0 mol %, respectively, and ZEOSPAN 8030 (trade name)available from Nippon Zeon Co.; as the epichlorohydrin rubber, e.g.,GECHRON 3106 (trade name) available from Nippon Zeon Co., Ltd.; as theacrylonitrile-butadiene rubber, e.g., DN 401 (trade name) available fromNippon Zeon Co., Ltd.; and as the blowing agent of an azodicarbonamidetype, e.g., VINYFOR AC (trade name) available from Eiwa Chemical Ind.Co., Ltd.

In the present invention, there are no particular limitations concerninga method for preparing the rubber composition from the above respectivecomponents. For example, what is suitable may be selected from knownmethods in accordance with raw materials to be used, composition and soforth. Specifically, for example, the prescribed components such as therubber component, the blowing agent, the conducting agent, thevulcanizing agent and the vulcanization accelerator may be kneaded bymeans of, e.g., a closed kneading machine such as a Banbury mixer or akneader to prepare the rubber composition.

An example of a vulcanizing forming system usable in the presentinvention is shown in FIG. 3. This system is constituted of an extruder11, a microwave vulcanizing unit (which is referred to also as a UHFvulcanizing unit) 12 as a warming and heating means, a hot-airvulcanizing unit (which is referred to also as an HAV vulcanizing unit)13 which is a hot-air heating means used as needed, a take-off gear 14,a cooling bath 15, a gauge cutter 16 and an automatic core materialpress-fit machine 17.

The rubber composition described above, having been prepared by kneadingmaterials by means of, e.g., a closed kneader such as a Banbury mixer ora kneader, is shaped into a ribbon by using an open roll and a ribbonsshaping and sheeting machine (not shown), and thereafter introduced intothe extruder 11. The UHF vulcanizing unit 12 has a mesh belt coated withpolytetrafluoroethylene (PTFE) or rollers covered with PTFE, and anunvulcanized rubber composition tube extruded from the extruder 11 isconveyed thereon, and while being conveyed, is irradiated withmicrowaves and heated so as to be foamed and vulcanized (orfoaming-vulcanized), thus a foamed rubber tube is formed. This foamedrubber tube is transported to the HAV vulcanizing unit 13. The UHFvulcanizing unit 12 and the HAV vulcanizing unit 13 are connectedthrough rollers covered with PTFE. The HAV vulcanizing unit 13 hasrollers covered with PTFE, and the foamed rubber tube is conveyedthereon and, while being conveyed, exposed to hot air and heated, andfurther vulcanized. The foamed rubber tube is taken off by means of thetake-off gear 14. Immediately after discharged from the take-off gear14, the tube is cooled in the cooling bath 15, and then cut in desiredsize by means of the gauge cutter 16. Thereafter, a core material issubsequently press-fitted into the conductive rubber tube by means ofthe automatic core material press-fit machine 17. Thus a foamed rubbertube having conductivity is prepared.

The UHF vulcanizing unit 12, the HAV vulcanizing unit 13, the take-offgear 14, the cooling bath 15, the gauge cutter 16 and the automatic corematerial press-fit machine 17 are, in this embodiment, 4 m, 6 m, 1 m, 1m, 1.5 m and 2 m, respectively. The distance between the UHF vulcanizingunit 12 and the HAV vulcanizing unit 13 and the distance between the HAVvulcanizing unit 13 and the take-off gear 14 are each so set as to befrom 0.1 to 1.0 m.

Subsequently, the foamed rubber tube is transported to the HAVvulcanizing unit 13 and, while being transported, heated in a hot-airfurnace of the HAV vulcanizing unit 13 to complete the vulcanization.There are no particular limitations on heating conditions in the hot-airfurnace of the HAV vulcanizing unit 13. Usually, such hot-air heatingmay preferably be carried out at 150 to 300° C. for 2 minutes to 10minutes. In addition, the hot-air furnace of the HAV vulcanizing unit 13may preferably be one having a gas furnace as a heat source. Inasmuch asthe hot-air furnace has a gas furnace as a heat source, a uniform stateof heating is achieved in virtue of water vapor generated in a slightquantity at the time of gas combustion.

The foamed rubber tube obtained after the vulcanization has beencompleted is taken off by means of the take-off gear 14 and, immediatelyafter discharged from the take-off gear 14, cooled in the cooling bath15, and then cut in desired size by means of the gauge cutter 16.

In particular, in the first-object invention, in the above vulcanizingforming system, the unvulcanized rubber composition tube formed byextruding the rubber composition into a tube by means of the extruder 11is, immediately after it has been extruded form the extruder 11,transported to the interior of the UHF vulcanizing unit 12, and istransported at a transport speed (or a feed rate) of from 0.5 to 3.0m/min through the interior of the UHF vulcanizing unit. In the interiorof the UHF vulcanizing unit 12, the tube is irradiated with microwaveshaving preferably an irradiation output of from 0.3 to 3.0 kW, by usinga microwave irradiator having a microwave irradiation zone of 4 m orless in length, to foam and vulcanize the rubber composition tube toform the foamed rubber tube.

The microwave irradiation zone is 4 m or less in length, and maypreferably be set to be 3 m or less in length. Then, the limit of thelength is considered to be about 1 m. As long as the microwaveirradiation zone is set to be 4 m or less in length, a uniform andstable state of foaming is obtained to create a uniform measure of theinner diameter. In the case of about 1 m as the limit, there is apossibility of sparking, and it is not practical. The transport speed isfrom 0.5 to 3.0 m/min, and may preferably be set at from 1.0 to 3.0m/min. As long as the transport speed is set at 0.5 m/min or more, amore stable state of vulcanization is obtained. Also, as long as thetransport speed is set at 3.0 m/min or less, a more stable state offoaming is obtained to create a uniform measure of the inner diameter.The microwave irradiation output may preferably be set at from 0.3 to3.0 kW, and more preferably from 0.3 to 2.0 kW. As long as the microwaveirradiation output is set at 0.3 kW or more, sufficient irradiation canbe effected even where the system is set up to be short. On the otherhand, as long as the microwave irradiation output is set at 3.0 kW orless, the tube can easily be prevented from being heated in excess,enabling the control to be facilitated even where a conductive rubberroller whose inner diameter is required to have a precise measure isproduced.

In the first-object invention, the foamed rubber tube thus formed byfoaming and vulcanization is also required to have an inner diameter (b)which is set to be smaller by from 20 to 35%, and preferably by from 20to 30%, than the outer diameter (a) of the conductive core material overthe whole region in the lengthwise direction of the conductive rubberroller. If less than 20%, a problem may occur such that the foamedrubber tube comes off the conductive core material. If more than 35%, aproblem may occur such that the conductive core material cannot bepress-fitted.

After the foamed rubber tube has been cut by means of the gauge cutter16, the conductive core material not coated with an adhesive such as ahot-melt adhesive or a vulcanizing adhesive is press-fitted into theinner-diameter part of the foamed rubber tube by means of the automaticcore material press-fit machine 17 so as to be covered with the foamedrubber tube having conductivity.

In particular, in the second-object invention, the microwaves maypreferably be at an intensity of from 0.5 to 3.0 kW in the above UHFvulcanization. If the intensity is less than 0.5 kW, the temperaturedoes not rise, and hence both the vulcanization and the foaming tend tobe insufficient. On the other hand, if irradiated at an intensity ofmore than 3.0 kW, the rubber is heated to 250° C. or more to becomevulcanized in excess, and further is in danger of ignition. This isundesirable not only in view of quality but also in respect ofproduction. In this regard, the temperature of the heating atmosphere ofthe UHF vulcanization is so controlled that the ratio of initialvulcanizing time T10 to initial foaming time Tp10, T10/Tp10, of therubber layer is from 1 or more to less than 3 and the T10 is within 90seconds. When setting temperature conditions in such a manner, thefoaming and vulcanization of the rubber layer can proceed in a wellbalanced state and a rubber tube free from foaming non-uniformity can beproduced. More specifically, if the temperature of the atmosphere bringsT10/Tp10 to less than 1, the vulcanization proceeds faster than thefoaming to make it difficult to form cells. If, on the other hand, thetemperature of the atmosphere brings T10/Tp10 to 3 or more, the foamingreaction proceeds faster than the vulcanization reaction. In particular,in the UHF vulcanizing furnace, the whole rubber is uniformly heatedwith microwaves at a high rate, and hence the foaming reaction israpidly accelerated. However, since T10/Tp10 is 3 or more, thevulcanization can not follow the foaming to make it difficult to formcells uniformly. In particular, where the temperature of the rubber tubeis higher than the temperature of the atmosphere, the surface of therubber tube radiates heat to produce a temperature difference betweenthe surface and the interior. As a result, the vulcanization proceedsslowly in the vicinity of the surface, and hence foaming non-uniformitytends to come about in the vicinity of the surface.

The temperature of the heating atmosphere of the UHF vulcanizing furnaceis also required to be set and managed at such a temperature that theT10 is within 90 seconds. With a temperature at which the T10 is morethan 90 seconds, the vulcanization does not proceed sufficiently in theUHF vulcanizing furnace and the vulcanization proceeds from the outsideto the inside in the HAV vulcanization. Hence, the rubber tube comes tohave larger cells on the outer-diameter side. Further, where themicrowaves are set at a high output, the temperature may differ greatlybetween the rubber tube surface and the interior so as to create foamingnon-uniformity.

In addition, in the second-object invention, the rubber layer has a gasgeneration rate of from 2 ml/g·min to 4 ml/g·min at 170° C. to 230° C.When the rubber layer temperature, i.e., the temperature of the heatingatmosphere in the UHF vulcanizing furnace is so controlled as to givethis gas generation rate, the foaming reaction can be completed in thesystem used in the second-object invention. If the gas generation rateis less than 2 ml/g·min, the foaming may become insufficient. If, on theother hand, more than 4 ml/g·min, outgassing may occur. Also, the foamcells are controlled to be uniform and be 0.3 mm or less in diameter byproperly adjusting the T10/Tp10, the T10 and the gas generation rate asshown above. A case in which the cells are more than 0.3 mm in diameteris undesirable because, in the transfer roller, marks of cells tend toremain on the photosensitive drum.

In particular, in the third-object invention, the dielectric losscoefficient εr·tan δ in the unvulcanized rubber of the rubber layer isfrom 0.3 to 0.5. This defines the range within which the step ofvulcanization and foaming in virtue of the irradiation with microwavesproceeds well in producing the conductive rubber roller such as atransfer roller having a rubber layer containing a polar rubberapplicable in the third-object invention. If the dielectric losscoefficient deviates from this range, e.g., if it is less than 3, theheating by microwave irradiation is insufficient and the vulcanizationdoes not proceed or is incomplete. If, on the other hand, more than 0.5,the heating may become excessive so that there is a fear that the rubberlayer deteriorates due to heat.

In the third-object invention, the irradiation with microwaves isrequired to be carried out using microwaves of 2,450±50 MHz in the UHFvulcanizing unit 12, which is set at an in-furnace atmospheretemperature of, e.g., 200° C. When using microwaves of 2,450±50 MHz,irradiation non-uniformity is reduced and the rubber tube can beirradiated in good efficiency. The hot air in the UHF vulcanizingfurnace may preferably be at a temperature of from 150° C. to 250° C.,and particularly from 180° C. to 230° C.

In particular, in the fourth-object invention, the rubber tube extrudedfrom the extruder 11 is required to be transported on a mesh belt coatedwith PTFE. In the mesh belt, there are no particular limitationconcerning its base material, provided that its surface is required tobe coated with PTFE so as not to adhere the rubber layer and also that amaterial having small heat capacity and heat resistance is preferred inorder to prevent temperature non-uniformity at contact portions.Although there are also no particular limitation concerning the shape ofmesh openings of the mesh belt, a shape such as a lattice shaperesistant to heating conditions and a certain degree of tension is oftenused.

The mesh belt is so made up that the ratio of outer diameter A (mm) ofthe rubber layer after the vulcanization to mesh opening percentage B(%) of the mesh belt, A/B, is from 0.2 or more to 0.4 or less. Inasmuchas the ratio is set to be within this range, the area in contact withthe mesh belt can be minimized and the rubber layer can be made freefrom foaming non-uniformity. If this ratio deviates from this range,e.g., if the A/B is less than 0.2, the mesh opening percentage withrespect to the tube outer diameter is large and the contact area issmall, but the mass of the rubber layer applied to the contact portionsbecomes large. Hence, mesh contact marks may seriously remain on therubber layer because the viscosity is reduced at the time ofvulcanization. If, on the other hand, it is more than 0.4, the meshopening percentage with respect to the tube outer diameter is so largeas to raise a problem in the circulation of hot air in the UHFvulcanizing furnace.

In particular, in the fifth-object invention, the output per microwaveoscillator is required to be set at from 0.1 to 1.5 kW, and preferablyfrom 0.15 to 1.0 kW. As long as the microwave irradiation output is setat 0.1 kW or more, sufficient irradiation can be effected even where thesystem is set up to be short. On the other hand, as long as themicrowave irradiation output is set at 1.5 kW or less, the tube can beeasily prevented from being heated in excess, enabling the control to befacilitated even where a conductive rubber roller required to undergouniform foaming is produced. It is preferable for the microwaveirradiator to use two or four microwave oscillators having an output offrom 0.1 to 1.5 kW per oscillator. It is more preferable to use fourmicrowave oscillators each having an output of from 0.1 to 1.5 kW. Ifone oscillator or three oscillators each having an output of from 0.1 to1.5 kW is/are used, the microwaves may be reflected irregularly in theunit to tend to make it difficult to effect uniform vulcanization andfoaming. If on the other hand five or more oscillators each having anoutput of from 0.1 to 1.5 kW are used, the tube may be irradiated withmicrowaves in excess to tend to bring about a non-uniformly foamedstate, and further a problem may be raised in that the roller has aresistivity higher than the desired resistivity.

In the fifth-object invention, in the above vulcanizing forming system,the unvulcanized rubber composition tube formed by extruding the rubbercomposition into a tube by means of the extruder 11 is, immediatelyafter it has been extruded form the extruder 11, transported to theinterior of the UHF vulcanizing unit 12, and is conveyed at a transportspeed of from 0.5 to 3.0 m/min through the interior of the UHFvulcanizing unit. In the interior of the UHF vulcanizing unit 12, thetube is irradiated with microwaves by using a microwave irradiatorhaving a microwave irradiation zone of 4 m or less in length, preferablyby using the microwave irradiator using two or four microwaveoscillators having an output of from 0.1 to 1.5 kW per oscillator, tofoam and vulcanize the rubber composition tube to form the foamed rubbertube.

In the fifth-object invention, the transport speed is from 0.5 to 3.0m/mini and is more preferably set at from 1.0 to 3.0 m/min. As long asthe transport speed is set at 0.5 m/min or more, a more stable state ofvulcanization is obtained. Also, as long as the transport speed is setat 3.0 m/min or less, a more stable state of foaming is obtained to givea uniform measure of the inner diameter. Also, the microwave irradiationzone is 4 m or less in length, and is preferably set to be 3 m or lessin length. The limit of the length is considered to be about 1 m takingthe possibility of sparking into account. As long as the microwaveirradiation zone is set to be 4 m or less in length, a uniform andstable state of foaming is obtained to give a uniform measure of theinner diameter. Also, the tube is cut by means of the gauge cutter 16,and thereafter, the conductive core material is subsequentlypress-fitted into the inner-diameter part of the foamed rubber tube bymeans of the automatic core material press-fit machine 17 so as to becovered with the foamed rubber tube having conductivity. The conductivecore material used here may be either one coated with an adhesive suchas a hot-melt adhesive or a vulcanizing adhesive, or one not coated withany adhesive.

Subsequently, this roller-shaped form is set on a grinder (not shown),and is ground under given grinding conditions to produce a conductiverubber roller having a given outer diameter.

The conductive rubber roller obtained may be used as a base layer memberto produce a roller for electrophotographic apparatus, such as acharging roller, a developing roller or a transfer roller.

In addition, for example, the developing roller and the charging rollermay be optionally provided, on the peripheral surface of the foamedrubber layer of the conductive rubber roller, with layers for impartingdesired functions, such as a bleed-out preventive layer which preventsthe low-molecular weight components and compounded chemicals such asstearic acid from bleeding out of the foamed rubber layer, an electrodelayer, an electrical resistance control layer which controls electricalproperties, and a cover layer provided in order for the photosensitivemember not to be scratched or contaminated. As methods for providing thebleed-out preventive layer, the electrode layer, the electricalresistance control layer, the cover layer and so forth, known methodsare available as exemplified by a method using coating fluids, such asdip coating or roll coating, and a method in which a simultaneouslyformed multi-layer seamless tube is applied.

For example, the transfer roller may be optionally provided, on theperipheral surface of the foamed rubber layer of the conductive rubberroller, with layers for imparting desired functions, such as a bleed-outpreventive layer which prevents low-molecular weight components andcompounded chemicals such as stearic acid from bleeding out of thefoamed rubber layer, an electrical resistance control layer whichcontrols electrical properties, and a surface property control layerwhich controls surface properties in order to improve properties oftransporting transfer mediums. These layers may be formed by the samemethods as in those of the developing roller and charging roller. Also,where the conductive rubber roller has the desired performance, it maybe used as the transfer roller as it is.

The present invention is described below in greater detail by givingExamples. In the Examples, while the transfer roller is particularlydescribed, the present invention is by no means limited only to thetransfer roller, and is also applicable to the charging roller and thedeveloping roller.

EXAMPLES 1-1 TO 1-5 & COMPARATIVE EXAMPLES 1-1 TO 1-5

Conductive rubber rollers (FIG. 1) for demonstrating the presentinvention were produced in the following way.

75 parts by mass of acrylonitrile-butadiene rubber (DN401, trade name,available from Nippon Zeon Co., Ltd.), 23 parts by mass ofepichlorohydrin rubber (GECHRON 3106, trade name, available from NipponZeon Co., Ltd.), 2 parts by mass of ethylene oxide-propylene oxide-allylglycidyl ether terpolymer (ZEOSPAN 8030, trade name, available fromNippon Zeon Co., Ltd.), 4 parts by mass of azodicarbonamide (VINYFOR AC,trade name, available from Eiwa Chemical Ind. Co., Ltd.), 1 part by massof stearic acid (LUNAC S20, trade name, available from Kao Corporation),5 parts by mass of zinc oxide (Zinc White JIS 1, trade name, availablefrom Hakusui Chemical Industries, Ltd.) and 10 parts by mass of carbon(ASAHI 35, trade name, available from Asahi Carbon Co., Ltd.) werekneaded by means of a Banbury mixer, and the kneaded product was shapedinto a ribbon by using an open roll and a ribbon shaping and sheetingmachine. This rubber composition shaped into a ribbon was introduced inthe extruder 11 (manufactured by Micro Denshi Co., Ltd.) of thevulcanizing forming system shown in FIG. 3, and unvulcanized rubbercomposition tubes were extruded under various conditions.

The rubber composition tubes thus obtained were each heated by means ofthe UHF vulcanizing unit 12 (manufactured by Micro Denshi Co., Ltd.) ina microwave irradiation zone of 4 m and under conditions shown in Tables1-1 and 1-2, to effect foaming and vulcanization. The foamed tubeobtained was taken off by means of the take-off gear 14. Immediatelyafter discharged out of the take-off gear 14, the tube was cooled in thecooling bath 15, and then cut in desired size by means of the gaugecutter 16 to produce a foamed rubber tube of 16.0 mm in outer diameter,4.2 mm in inner diameter and 250 mm in length. Thereafter, subsequently,a conductive core material of 6 mm in outer diameter, having not beencoated with any adhesive was press-fitted to the inner-diameter part ofthe foamed rubber tube by means of the automatic core material press-fitmachine 17 to produce a roller-shaped form having the foamed rubber tubeas a foamed rubber layer. This roller-shaped form was set on a grinder(not shown) fitted with a grindstone GC80, and was so ground as to havean outer diameter of 17 mm, under grinding conditions of a rotationalspeed of 2,000 rpm and a feed rate of 0.5 m/minute. Thus, conductiverubber rollers were produced.

The measurement of aspect ratios of inner and outer diameters of eachfoamed rubber tube at the time of irradiation with microwaves, theevaluation of cell diameter distribution of each foamed rubber tube, theevaluation of press-fit performance, the measurement of hardnessnon-uniformity of each conductive rubber roller and the measurement ofelectrical resistance non-uniformity of each conductive rubber roller inthe Examples and Comparative Examples were made in the following way.Results obtained are shown in Tables 1-1 and 1-2.

How to Measure Outer Diameter of Conductive Core Material and InnerDiameter of Foamed Rubber Tube:

The outer diameter (a) of the conductive core material and the innerdiameter (b) of the foamed rubber tube were each measured with a verniercaliper and a pin gauge to determine the proportion of the differencebetween them [{(a−b)/a}×100]. It is desirable that the proportion ofsaid difference is from 20 to 35%.

Press-Fit Performance:

When the conductive core material was press-fitted into the foamedrubber tube, a case in which the conductive core material was able to bepress-fitted was evaluated as “A”, a case in which the conductive corematerial was able to be press-fitted, but the foamed rubber tube wasbroken or came off was evaluated as “B”, and a case in which theconductive core material was unable to be press-fitted at all wasevaluated as “C”.

How to Measure Aspect Ratios of Inner and Outer Diameters of FoamedRubber Tube:

The foamed rubber tube was cut at arbitrary positions, and the sectionswere projected by using a projector (Profile Projector V-12B, tradename, manufactured by Nikon Corporation), and the maximum (t_(max)) andminimum (t_(min)) of each of the inner diameter and outer diameter ofeach of the projected sections were measured and the ratio oft_(max)/t_(min) was determined. It is preferable that this ratio isclose to 1.

How to Measure Hardness Non-Uniformity of Conductive Rubber Roller:

Using a hardness meter (Asker-C type; load: 4.9 N), the hardness of thefoamed rubber layer of the conductive rubber roller was measured at fourspots (one spot for each 90 degrees in the peripheral direction at anarbitrary position). The difference between the maximum value andminimum value of the hardness was determined and regarded asnon-uniformity of hardness. It is preferable that the non-uniformity ofhardness is close to 0.

How to Evaluate Cell Diameter Distribution of Foamed Rubber Tube:

The foamed rubber tube was cut at arbitrary positions, and its sectionswere recorded by using a video microscope (Digital Microscope VH-8000,trade name, manufactured by Keyence Corporation). The difference inmeasure between the cell diameter on the outer-diameter side and thecell diameter on the inner-diameter side was ascertained by measuringthem with a gauge displayed on a monitor of the video microscope. It ispreferable that there is no difference between the cell diameter on theouter-diameter side (D_(ou)) and the cell diameter on the inner-diameterside (D_(in)). Evaluation was made according to the following criteria.

A: There is no difference; (|D_(ou)−D_(in)|/D_(ou))≦1.5 or(|D_(ou)−D_(in)|/D_(in))≦1.5.

B: There is a little difference; 1.5<(|D_(ou)−D_(in)|/D_(ou))≦2.0 or1.5<(|D_(ou)−D_(in)|/D_(in))≦2.0.

C: There is a difference; (|D_(ou)−D_(in)|/D_(ou))>2.0 or(|D_(ou)−D_(in)|/D_(in))>2.0.

How to Measure Non-Uniformity of Electrical Resistance of ConductiveRubber Roller:

After being left standing for 48 hours in an environment of 23° C./55%RH, the conductive rubber roller was brought into pressure contact witha drum 30 mm in outer diameter made of aluminum under the application ofa load of 4.9 N to each of both end portions of the shaft of the roller.In the state this was rotated, a voltage of 2 kV was applied between theconductive core material of the conductive rubber roller and the drummade of aluminum to measure the electrical resistance. The difference inresistance value between the maximum value R_(max) and the minimum valueR_(min), R_(max)−R_(min), thus measured was expressed by the differencein power [log(R_(max)/R_(min))]. It is preferable that thenon-uniformity of the electrical resistance is of the power of less than1.2.

As shown in Table 1-1, in Examples 1-1 to 1-5, tubes are irradiated withmicrowaves at a total irradiation output of from 0.3 to 3.0 kW whilethey are transported at a transport speed of from 0.5 to 3.0 m/min inthe microwave vulcanizing unit having a microwave irradiation zone of 4m or less. It is seen that in such cases, the conductive core materialsare satisfactorily press-fitted into the foamed rubber tubes (goodpress-fit performance), the aspect ratios of the inner and outerdiameters of each foamed rubber tube are as small as 1.05 or less, andalso the cell diameter distributions are uniform. It is further seenthat the conductive rubber rollers are small in the non-uniformity ofhardness in their peripheral directions, and also have thenon-uniformity of electrical resistance of the power as small as 1.05 orless.

On the other hand, in Comparative Examples 1-1 to 1-5, as shown in Table1-2, examples are cited in which the microwave irradiation output is setat 0.1 kW, 1.5 kW, 2.0 kW or 4.0 kW and the transport speed at 0.3 m/minor 3.5 m/min. In Comparative Example 1-1, the foamed rubber tube cameoff the conductive core material after press-fitted. In ComparativeExamples 1-3 and 1-4, the core materials was able to be press-fittedinto the foamed rubber tubes, but the tubes were broken or torn, andwere unable to be made up as conductive rubber rollers. Also, inComparative Examples 1-2 and 1-5, the foamed rubber tubes had so smallan inner diameter that the conductive core materials were unable to bepress-fitted. Further, it is seen that the cell diameter distribution ispoor and also the aspect ratios of the inner and outer diameters of eachfoamed rubber tube are larger than those in Examples. TABLE 1-1 Example1-1 1-2 1-3 1-4 1-5 Microwave irradiation output: (kW) 0.3 1.0 1.5 2.03.0 Transport speed: (m/min) 0.5 0.5 2.0 3.0 3.0 Conductive corematerial outer 5.0 6.0 10.0 8.0 6.0 diameter a: (mm) Foamed rubber tubeinner diameter b: 4.0 3.9 8.0 5.2 4.8 (mm) ((a − b)/a) × 100: (%) 20 3520 35 20 Press-fit performance: A A A A A Tube aspect ratio (outerdiameter): 1.01 1.01 1.05 1.03 1.01 Tube aspect ratio (inner diameter):1.00 1.01 1.02 1.03 1.02 Hardness non-uniformity: 0 0 1 1 0 Electricalresistance non-uniformity: 1.02 1.03 1.04 1.05 1.03 (power) Celldiameter distribution: A A A A A

TABLE 1-2 Comparative Example 1-1 1-2 1-3 1-4 1-5 Microwave irradiationoutput: (kW) 0.1 4.0 1.5 1.5 2.0 Transport speed: (m/min) 0.3 3.5 3.50.3 0.3 conductive core material outer 5.0 6.0 6.0 10.0 8.0 diameter a:(mm) Foamed rubber tube inner diameter b: 4.3 3.6 5.4 8.8 4.8 (mm) ((a −b)/a) × 100: (%) 15.0 40.0 10.0 12.0 40.0 Press-fit performance: B C B BC Tube aspect ratio (outer diameter): 2.1 2.3 2.6 2.5 3.1 Tube aspectratio (outer diameter): 3.0 2.1 2.5 2.6 2.6 Hardness non-uniformity: MMNM NM NM NM Electrical resistance non-uniformity: NM NM NM NM NM (power)Cell diameter distribution: C C C C BNM: Not measurable.

EXAMPLES 2-1 TO 2-9 & COMPARATIVE EXAMPLES 2-1 TO 2-6

Immediately after tubes were each discharged out of the take-off gearafter vulcanization and foaming, they were cut in desired size by meansof the gauge cutter to produce tubular conductive rubber forms.Subsequently, conductive core materials of from 4 to 10 mm in diametercoated with a hot-melt adhesive or a vulcanizing adhesive at theirdesired regions were press-fitted into the inner-diameter part of thetubular conductive rubber forms to produce roller-shaped forms. Theseforms were each set on a grinder (not shown) fitted with a grindstoneGC80, and were each so ground as to have an outer diameter of from 16 to20 mm, under grinding conditions of a rotational speed of 2,000 rpm anda feed rate of 500 mm/minute. Thus, conductive rubber rollers wereproduced.

In addition, formulation and parts by mass of materials used in each ofthe Examples and Comparative Examples are as follows: (by mass)Acrylonitrile-butadiene rubber (trade name: DN401LL; 84 parts  availablefrom Nippon Zeon Co., Ltd.) Epichlorohydrin rubber (trade name: GECHRON3106; 16 parts  available from Nippon Zeon Co., Ltd.) Conductive carbonblack (trade name: ASAHI #35; 10 parts  available from Asahi Carbon Co.,Ltd.) Zinc oxide (trade name: Zinc White JIS 2; available 5 parts fromHakusui Tech Co., Ltd.) Stearic acid (trade name: LUNAC S; availablefrom Kao 1 part Corporation) Thiazole type accelerator: dibenzothiazyldisulfide 2 parts (trade name: NOCCELER DM-P; available from Ohuchi-Shinko Chemical Industrial Co., Ltd.) Thiuram disulfide typeaccelerator: 2.5 parts   tetrakis(2-ethylhexyl)thiuram disulfide (tradename: NOCCELER TOT-N; molecular weight: 633.18; available fromOhuchi-Shinko Chemical Industrial Co., Ltd.) Sulfur (trade name: SULFAXPMC; available from 2 parts Tsurumi Kagaku Kogyo K.K.) Azodicarbonamide(trade name; CELLMIC M257; available 4 parts from Sankyo Kasei Co.,Ltd.) Urea (trade name; CELLMIC M258; available from Sankyo 2 partsKasei Co., Ltd.)

In respect of the rubber layers made up in the above formulation asrubber materials, evaluation was made by the following methods changingUHF vulcanizing furnace atmosphere temperature, transport speed andmicrowave output. The results are shown in Tables 2-1 and 2-2.

How to Measure T10/Tp10:

Moving Die Rheometer MDR2000 (manufactured by Alpha Technologies, Inc.)was used, and a given amount of unvulcanized rubber was placed in a dieset at a given temperature, to make measurement for vulcanization andfoaming curves. The value of T10/Tp10 was calculated from the initialvulcanizing time T10 and initial foaming time Tp10 obtained.

How to Measure Rubber Temperature at the Time of Microwave Irradiation:

A fluorescent thermometer (a fluorescence type fiber thermometerFL-2000, manufactured by Anritsu Meter Co., Ltd.) was used, and adetector of the fluorescent thermometer was inserted to the interior ofthe unvulcanized rubber tube extruded from the extruder, and transportedto the interior of the UHF vulcanizing furnace together with theunvulcanized rubber tube, thus the temperature was measured.

How to Measure Gas Generation Rate:

A gas tracer instrument (Gas Tracer 250, manufactured by Eiwa ChemicalInd. Co., Ltd.) was used, and 5 g of unvulcanized rubber to be used and10 ml of liquid paraffin were put into a test tube. This test tube wasimmersed in an oil bath for 30 minutes which was set at arbitrarytemperature within the temperature range of from 170° C. to 230° C. Gasgeneration quantity was measured at intervals of 10 seconds after theimmersion. To find the gas generation rate, the gas generation quantityat the time the gas generation quantity reached equilibrium was dividedby the time taken until the equilibrium was reached.

How to Measure Foam Cell Diameter:

The rubber tube was cut at arbitrary positions, and the sections wereobserved with a video microscope (Digital Microscope VH-8000, tradename, manufactured by Keyence Corporation). To make measurement, thefoamed rubber tube was observed at 50 magnifications over the wholeregion from the inner-diameter side to the outer-diameter side, and thediameter of each cell was measured at N=30. The maximum value of themeasured values was regarded as the cell diameter (width) of the rubbertube.

How to Measure Non-Uniformity of Hardness:

Using a hardness meter (Asker-C type; load: 4.9 N), the hardness of thetube made into the conductive roller was measured at four spots (onespot for each 90 degrees in the peripheral direction at an arbitraryposition). The difference between the maximum value and minimum value ofthe hardness was expressed as hardness difference. It is preferable thatthe hardness difference is 0 or close to 0, or the closer to 0 thebetter.

How to Measure Non-Uniformity of Electrical Resistance:

To measure the electrical resistance of the roller, after being leftstanding for 48 hours in an environment of N/N (23° C./55% RH), theconductive rubber roller was brought into pressure contact with a drum30 mm in outer diameter made of aluminum under application of a load of4.9 N to each of both end portions of the shaft of the roller. In thestate this was rotated, a voltage of 2 kV was applied between the shaftand the aluminum drum. The ratio of the maximum to the minimum of theresistance value thus measured was expressed as peripheralnon-uniformity of resistance. It is preferable that the peripheralnon-uniformity is 1.6 or less, and particularly preferably less than1.2. TABLE 2-1 Example 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 UHFvulcanizing furnace atmosphere temperature: (° C.) 200 200 200 180 180180 170 170 170 Transport speed: (m/min) 1.2 2.4 3.2 1.2 2.4 3.2 1.2 2.43.2 Microwave output: (kw) 1.0 2.0 3.0 1.0 2.0 3.0 1.0 2.0 3.0 Rubberlayer ultimate temperature: (° C.) 205 200 203 185 180 178 175 173 176Gas generation rate: (ml/g · min) 3.5 3.5 3.5 3.0 3.0 3.0 2.2 2.2 2.2(Gas generation level: (ml/g) 16 16 16 14 14 14 12 12 12 Initialvulcanizing time T10: (sec) 18 18 18 33 33 33 49 49 49 Initial foamingtime Tp10: (sec) 13 13 13 19 19 19 25 25 25 T10/Tp10: 1.38 1.38 1.381.74 1.74 1.74 1.96 1.96 1.96 Cell diameter: (mm) 0.24 0.22 0.22 0.240.21 0.23 0.25 0.26 0.26 Foaming non-uniformity: A A A A A A A A AElectrical resistance peripheral non-uniformity: 1.04 1.07 1.06 1.051.07 1.09 1.09 1.10 1.11 Hardness difference: 0.8 1.1 0.9 1.2 1.4 1.21.6 1.6 1.5

TABLE 2-2 Comparative Example 2-1 2-2 2-3 2-4 2-5 2-6 UHF vulcanizingfurnace atmosphere temperature: (° C.) 160 160 160 130 130 130 Transportspeed: (m/min) 1.2 2.4 3.2 1.2 2.4 3.2 Microwave output: (kw) 1.0 2.03.0 1.0 2.0 3.0 Rubber layer ultimate temperature: (° C.) 160 158 162125 130 128 Gas generation rate: (ml/g · min) 1.3 1.3 1.3 0.2 0.2 0.2Gas generation level: (ml/g) 10 10 10 4 4 4 Initial vulcanizing timeT10: (sec) 85 85 85 506 506 506 Initial foaming time Tp10: (sec) 28 2828 99 99 99 T10/Tp10: 3.04 3.04 3.04 5.11 5.11 5.11 Cell diameter: (mm)0.30 0.31 0.32 0.35 0.34 0.36 Foaming non-uniformity: B B B C C CElectrical resistance peripheral non-uniformity: 1.12 1.15 1.14 1.341.32 1.37 Hardness difference: 3 2.5 2.8 5 5 5

Re Examples 2-1 to 2-9:

As shown in Table 2, the ultimate temperature of the rubber layer iscontrolled by the temperature of the atmosphere and the microwave outputin the UHF vulcanizing furnace. The condition for measurement wasadjusted to the ultimate temperature of each rubber layer and gasgeneration rates during foaming were measured with the gas tracerinstrument, where it was seen that the gas generation rates are withinwhat was required in the present invention. Thus, the rubber layers aresatisfactorily foamed, and the cells are uniform and free fromnon-uniformity. Further, the hardness difference is small, and thenon-uniformity of electrical resistance is of the power of 1.6 or less.

Regarding Comparative Examples 2-1 to 2-6:

In Comparative Example 2-1, the value of T10/Tp10 deviates from what isrequired in the present invention, and the vulcanization occurred laterthan the foaming. Hence, the cells formed were non-uniform, andnon-uniformity of foaming came about. Also, in Comparative Example 2-4,the temperature of the atmosphere was set at 130° C., where both the T10and the T10/Tp10 deviated from what was required in the presentinvention, and the vulcanization occurred greatly later than thefoaming, so that great non-uniformity of foaming was seen. In otherComparative Examples, the vulcanization and foaming in some case werenot completed in the UHF vulcanizing furnace or HAV vulcanizing furnacein the system presented in the present invention, and also in somecases, not only suitable rubber tube were not obtainable but alsorollers were not producible. In the cases in which rollers wereproducible, great foaming non-uniformity of foaming came about, and thefoam cells were more than 0.3 mm in diameter in some cases. Hence,non-uniformity of hardness and electrical resistance occurred seriously.

EXAMPLES 3-1 TO 3-3 & COMPARATIVE EXAMPLES 3-1 TO 3-3

Immediately after discharged out of the take-off gear subsequently tovulcanization and foaming, tubes were each cut in a desired size bymeans of the gauge cutter to produce tubular conductive rubber forms.Then, conductive core materials of from 4 to 10 mm in diameter coatedwith a hot-melt adhesive or a vulcanizing adhesive at their desiredregions, were press-fitted into the inner-diameter part of the tubularconductive rubber forms to produce roller-shaped forms. These forms wereeach set on a grinder (not shown) fitted with a grindstone GC80, andwere each so ground as to have an outer diameter of from 16 to 20 mmunder grinding conditions of a rotational speed of 2,000 rpm and a feedrate of 500 mm/minute. Thus, conductive rubber rollers were produced.

Materials used in the present Examples and Comparative Examples were asfollows:

Acrylonitrile-butadiene rubber (trade name: DN401LL; available fromNippon Zeon Co., Ltd.).

Epichlorohydrin rubber (trade name: GECHRON 3106; available from NipponZeon Co., Ltd.).

Conductive carbon black (trade name: ASAHI #35; available from AsahiCarbon Co., Ltd.).

Sulfur (trade name: SULFAX PMC; available from Tsurumi Kagaku KogyoK.K.).

Thiazole type accelerator: dibenzothiazyl disulfide (trade name:NOCCELER DM-P; available from Ohuchi-Shinko Chemical Industrial Co.Ltd.).

Thiuram type accelerator: tetrakis(2-ethylhexyl)thiuram disulfide,(trade name: NOCCELER TOT-N; molecular weight: 633.18; available fromOhuchi-Shinko Chemical Industrial Co., Ltd.).

Azodicarbonamide (trade name; CELLMIC M257; available from Sankyo KaseiCo., Ltd.).

Urea (trade name; CELLMIC M258; available from Sankyo Kasei Co., Ltd.).

The tubes were obtained by using the production process as shown aboveand according to the formulation and parts by mass as shown in Table3-1, to form the conductive rollers.

Evaluation methods in the present invention are described next.

How to Measure Dielectric Loss Coefficient εr·tan δ:

The dielectric loss coefficient εr·tan δ was measured by using ENASeries Network Analyzer E5071B (300 kHz-8.5 MHz), manufactured byAgilent Technologies, and by bringing an electrode into contact with ameasuring sample and irradiating the rubber with microwaves. Inaddition, a measurement frequency was 2,450 MHz, and unvulcanized rubberwas used in an environment of a normal temperature of 23° C. The resultsare shown in Table 3-1.

How to Measure Rubber Temperature in UHF Vulcanizing Furnace at the Timeof Microwave Irradiation:

A fluorescent thermometer (a fluorescence type fiber thermometerFL-2000, manufactured by Anritsu Meter Co., Ltd.) was used, and adetector of the fluorescent thermometer was inserted into the interiorof the unvulcanized rubber tube extruded from the extruder, and wastransported to the interior of the UHF vulcanizing furnace together withthe unvulcanized rubber tube, thus the temperature was measured. Theresults are shown in Table 3-1.

How to Measure Hardness and Hardness Difference:

Using a hardness meter (Asker-C type; load: 4.9 N), the hardness of thetube made into the conductive roller was measured at four spots (onespot for each 90 degrees in the peripheral direction at an arbitraryposition). The average value was expressed as hardness, and thedifference between the maximum value and the minimum value of thehardness was expressed as hardness difference. It is preferable that thehardness difference is 0 or close to 0, or the closer to 0 the better.The results are shown in Table 3-1.

How to Ascertain Non-Uniformity of Foaming:

The rubber tube was cut at arbitrary positions, and the sections wereobserved with a video microscope (Digital Microscope VH-8000, tradename, manufactured by Keyence Corporation) to examine whethernon-uniformity of foaming occurred. It is preferable that nonon-uniformity of foaming is seen over the whole observation areas, inparticular, that there is no difference between the cell diameter on theouter diameter side and the cell diameter on the inner diameter side. Acase in which there is no difference is evaluated as “A”; a case inwhich there is a little difference, as “B”; and a case in which there isa difference, as “C”. The results are shown in Table 3-1. TABLE 3-1Example Comparative Ex. 3-1 3-2 3-3 3-1 3-2 3-3 Acrylonitrile-butadienerubber: 80 80 80 80 80 80 Epichlorohydrin rubber: 20 20 20 20 20 20Carbon black: 10 20 30 50 90 0 Sulfur: 2 2 2 2 2 2 Thiazole typeaccelerator: 2 2 2 2 2 2 Thiuram type accelerator: 2.5 2.5 2.5 2.5 2.52.5 Azodicarbonamide: 4 4 4 4 4 4 Urea: 2 2 2 2 2 2 Dielectric constantεr: 3.64 4.77 5.89 8.15 12.66 2.45 Dielectric power factor tanδ: 0.090.09 0.08 0.07 0.05 0.09 Dielectric loss coefficient εr · tanδ: 0.330.41 0.47 0.57 0.64 0.21 Rubber temp. in UHF vulcanizing furnace: 195210 223 240 — 160 Hardness (Asker C): 25 30 35 40 — 35 Hardnessdifference: 1 1 1 4 — 2 Foaming non-uniformity: A A A C — C

Regarding Examples 3-1 to 3-3:

As shown in Table 3-1, dielectric loss coefficients are within theproper range, so that the foaming non-uniformity and the hardnessdifference are small.

Regarding Comparative Examples 3-1 to 3-3:

Cases deviating from what is required in the present invention are givenas Comparative Examples. In all the cases, the dielectric losscoefficient deviates from that in the present invention. In ComparativeExample 3-1, in which the carbon black is in a large quantity, thenon-uniformity of foaming and the hardness difference are large, and inComparative Example 3-2, the rubber was seen to be heated in excess. Onthe other hand, in Comparative Example 3-3, in which no carbon black isadded, the rubber temperature does not sufficiently reach thedecomposition temperature of the blowing agent under irradiation withmicrowaves, so that the foaming is effected in the HAV vulcanizingfurnace to create non-uniformity of foaming in the peripheral direction.

EXAMPLES 4-1 TO 4-7 & COMPARATIVE EXAMPLES 4-1 TO 4-5

Immediately after discharged out of the take-off gear subsequently tovulcanization and foaming, tubes were each cut in a desired size bymeans of the gauge cutter to produce tubular conductive rubber forms.Subsequently, conductive core materials of from 4 to 10 mm in diametercoated with a hot-melt adhesive or a vulcanizing adhesive at theirdesired regions, were press-fitted into the inner-diameter part of thetubular conductive rubber forms to produce roller-shaped forms. Theseforms were each set on a grinder (not shown) fitted with a grindstoneGC80, and were each so ground as to have an outer diameter of from 16 to20 mm under grinding conditions of a rotational speed of 2,000 rpm and afeed rate of 500 mm/minute. Thus, conductive rubber rollers wereproduced.

Evaluation methods in the present invention are described below.

Outer Diameter of Tube Having Been Vulcanized:

The outer diameter of the rubber tube having been vulcanized wasmeasured at arbitrary positions with a digital vernier caliper(manufactured by Anritsu Meter Co., Ltd.) after vulcanization.Thereafter, the rubber tube was ground to have the desired outerdiameter, and the grinding level (mm) was found by subtracting the outerdiameter of the rubber tube having been ground from the outer diameterof the rubber tube having been vulcanized.

Mesh Belt Marks:

After the vulcanization, the rubber tube was cut at arbitrary positions,and marks of the mesh belt were ascertained by visual observation of thecut surface and the contact surface. A case in which the marks of themesh belt were 1 mm or less in size in the diameter direction wasevaluated as “no mesh belt mark”; and a case in which the marks of themesh belt were more than 1 mm in size, as “mesh belt marks are present”.

How to Ascertain Non-Uniformity of Foaming:

The rubber tube was cut at arbitrary positions, and the sections wereobserved with a video microscope (Digital Microscope VH-8000, tradename, manufactured by Keyence Corporation).

How to Measure Non-Uniformity of Hardness:

Using a hardness meter (Asker-C type; load: 4.9 N), the hardness of thetube made into the conductive roller was measured at four spots (onespot for each 90 degrees in the peripheral direction at an arbitraryposition). The difference between the maximum value and the minimumvalue of the hardness was expressed as hardness difference. It ispreferable that the hardness difference is 0 or close to 0, or thecloser to 0 the better.

How to Measure Non-Uniformity of Electrical Resistance:

To measure roller electrical resistance, after being left standing for48 hours in an environment of N/N (23° C./55% RH), the conductive rubberroller was brought into pressure contact with a drum 30 mm in outerdiameter made of aluminum under application of a load of 4.9 N to eachof both end portions of the conductive core material (mandrel or shaft)of the roller. In the state this was rotated, a voltage of 2 kV wasapplied between the shaft and the aluminum drum. The ratio of themaximum to the minimum of the resistance value thus measured wasexpressed as peripheral non-uniformity.

It is preferable that the peripheral non-uniformity is of the power ofless than 1.2.

Formulation and parts by mass of rubber materials used in the presentExamples and Comparative Examples are as follows: (by mass)Acrylonitrile-butadiene rubber (trade name: DN401LL; 84 parts  availablefrom Nippon Zeon Co., Ltd.) Epichlorohydrin rubber (trade name: GECHRON3106; 16 parts  available from Nippon Zeon Co., Ltd.) Conductive carbonblack (trade name: ASAHI #35; 10 parts  available from Asahi Carbon Co.,Ltd.) Zinc oxide (trade name: Zinc White JIS 2; 5 parts available fromHakusui Tech Co., Ltd.) Stearic acid (trade name: LUNAC S; availablefrom 1 part  Kao Corporation) Thiazole type accelerator: dibenzothiazyldisulfide 2 parts (trade name: NOCCELER DM-P; available from Ohuchi-Shinko Chemical Industrial Co., Ltd.) Thiuram disulfide typeaccelerator: 2.5 parts   tetrakis(2-ethylhexyl)thiuram disulfide (tradename: NOCCELER TOT-N; molecular weight: 633.18; available fromOhuchi-Shinko Chemical Industrial Co., Ltd.) Sulfur (trade name: SULFAXPMC; available from 2 parts Tsurumi Kagaku Kogyo K.K.) Azodicarbonamide(trade name; CELLMIC M257; 4 parts available from Sankyo Kasei Co.,Ltd.) Urea (trade name; CELLMIC M258; available from 2 parts SankyoKasei Co., Ltd.)

In respect of the rubber layers constituted of acrylonitrile-butadienerubber and epichlorohydrin rubber as rubber materials, provided in thepresent invention, some examples are given concerning the conditionsspecified in the present invention. The results are shown in Table 4-1.

It is seen from Table 4-1 that no mesh belt mark is seen, the foaming isuniform and free from non-uniformity, and as a result, the hardnessdifference is small and also the non-uniformity of electrical resistanceis of the power of 1.1 or less. Also, the grinding level is 2 mm orless, and this is also economically effective.

Cases deviating from the conditions specified in the present inventionare given as Comparative Examples. The results are shown in Table 4-2.In all the cases, the mesh bolt marks are seen, and as a result, thenon-uniformity of foaming, the hardness difference and the electricalresistance non-uniformity in the peripheral direction are large. Becauseof the non-uniformity of foaming, the grinding level also is increased.TABLE 4-1 Example 4-1 4-2 4-3 4-4 4-5 4-6 4-7 Tube outer diameter (A):(mm) 16 16 16 20 20 20 20 Mesh opening percentage (B): (%) 56 64 69 5664 69 79 Ratio A/B: 0.29 0.25 0.23 0.36 0.31 0.29 0.25 Mesh belt marks:none none none none none none none Grinding level (mm): 1.3 1.2 1.5 1.31.2 1.5 1.6 Foaming non-uniformity: none none none none none none noneHardness difference (Asker C): 1 0.8 1.2 1.3 0.8 1 •1 Electricalresistance non-uniformity 1.02 1.03 1.05 1.04 1.03 1.08 1.08 inperipheral direction:

TABLE 4-2 Comparative Example 4-1 4-2 4-3 4-4 4-5 Tube outer diameter(A): (mm) 16 16 16 16 16 Mesh opening percentage (B): (%) 11 25 83 85 91Ratio A/B: 1.45 0.64 0.19 0.19 0.18 Mesh belt marks: yes yes yes  yesyes Grinding level: (mm) 3 2.5 2.2 2.5 3 Foaming non-uniformity: yes yesyes* yes yes Hardness difference (Asker C): 6 4 3 5 7 Electricalresistance non-uniformity 1.2 1.3 1.1 1.4 1.3 in peripheral direction:*a little

EXAMPLES 5-1 TO 5-5 &, COMPARATIVE EXAMPLES 5-1 TO 5-5

Conductive rubber rollers (FIG. 1) which demonstrate the presentinvention were produced in the following way.

75 parts by mass of acrylonitrile-butadiene rubber (DN401, trade name,available from Nippon Zeon Co., Ltd.), 10 parts by mass ofepichlorohydrin rubber (GECHRON 3106, trade name, available from NipponZeon Co., Ltd.), 15 parts by mass of ethylene oxide-propyleneoxide-allyl glycidyl ether terpolymer (compositional proportion ofpropylene oxide: 1.30 mol %; compositional proportion of allyl glycidylether: 11.7 mol %; a trial product), 4 parts by mass of azodicarbonamide(VINYFOR AC, trade name, available from Eiwa Chemical Ind. Co., Ltd.), 1part by mass of stearic acid (LUNAC S20, trade name, available from KaoCorporation), 5 parts by mass of zinc oxide (Zinc White JIS 1, tradename, available from Hakusui Chemical Industries, Ltd.) and 10 parts bymass of carbon (ASAHI 35, trade name, available from Asahi Carbon Co.,Ltd.) were kneaded by means of a Banbury mixer, and the kneaded productobtained was shaped into a ribbon by using an open roll and a ribbonshaping and sheeting machine. This rubber composition shaped into aribbon was introduced in the extruder 11 (manufactured by Micro DenshiCo., Ltd.) of the vulcanizing forming system shown in FIG. 3, andunvulcanized rubber composition tubes were extruded under variousconditions.

The rubber composition tubes thus obtained were each heated by means ofthe UHF vulcanizing unit 12 (manufactured by Micro Denshi Co., Ltd.) ina microwave irradiation zone of 4 m and under conditions shown in Tables5-1 and 5-2, to effect foaming and vulcanization. The foamed tubeobtained was taken off by means of the take-off gear 14. Immediatelyafter discharged out of the take-off gear 14, the tube was cooled in thecooling bath 15, and then cut in a desired size by means of the gaugecutter 16 to produce a foamed rubber tube of 16.0 mm in outer diameter,4.2 mm in inner diameter and 250 mm in length. Thereafter, a conductivecore material of 6 mm in outer diameter was press-fitted into theinner-diameter part of the foamed rubber tube by means of the automaticcore material press-fit machine 17 to produce a roller-shaped formhaving the foamed rubber tube as a foamed rubber layer. Thisroller-shaped form was set on a grinder (not shown) fitted with agrindstone GC80, and was so ground as to have an outer diameter of 17 mmunder grinding conditions of a rotational speed of 2,000 rpm and a feedrate of 0.5 m/minute. Thus, conductive rubber rollers were produced.

The measurement of aspect ratios of inner and outer diameters of eachfoamed rubber tube, the evaluation of cell diameter distribution of eachfoamed rubber tube, the measurement of hardness non-uniformity of eachconductive rubber roller, the measurement of electrical resistance valueand environmental variation level of each conductive rubber roller andthe measurement of electrical resistance non-uniformity of eachconductive rubber roller in the above Examples and Comparative Exampleswere made in the following way. The results obtained are shown in Tables5-1 and 5-2.

How to Measure Aspect Ratios of Inner and Outer Diameters of FoamedRubber Tube:

The foamed rubber tube was cut at arbitrary positions under arbitraryconditions, and the sections were projected by using a projector(Profile Projector V-12B, trade name, manufactured by NikonCorporation), and the maximum (t_(max)) and minimum (t_(min)) of each ofthe inner diameter and outer diameter of each of the projected sectionswere measured and the ratio of t_(max)/t_(min) was determined. It ispreferable that this ratio is close to 1.

How to Measure Non-Uniformity of Hardness of Conductive Rubber Roller:

Using a hardness meter (Asker-C type; load: 4.9 N), the hardness of thefoamed rubber layer of the conductive rubber roller was measured at fourspots (one spot for each 90 degrees in the peripheral direction at anarbitrary position). The difference between the maximum value andminimum value of the hardness was determined and was regarded ashardness non-uniformity. It is preferable that the non-uniformity ofhardness is close to 0.

How to Evaluate Cell Diameter Distribution of Foamed Rubber Tube:

The foamed rubber tube was cut at arbitrary positions, and the sectionswere recorded by using a video microscope (Digital Microscope VH-8000,trade name, manufactured by Keyence Corporations). The difference inmeasure between the cell diameter on the outer-diameter side and thecell diameter on the inner-diameter side was ascertained by measuringthem with a gauge displayed on a monitor of the video microscope. It ispreferable that there is no difference between the cell diameter on theouter-diameter side (D_(ou)) and the cell diameter on the inner-diameterside (D_(in)). Evaluation was made according to the following criteria.

A: There is no difference; (|D_(ou)−D_(in)|/D_(ou))≦1.5 or(|D_(ou)−D_(in)|/D_(in))≦1.5.

B: There is a little difference; 1.5<(|D_(ou)−D_(in)|/D_(ou))≦2.0 or1.5<(|D_(ou)−D_(in)|/D_(in))≦2.0.

C: There is a difference; (|D_(ou)−D_(in)|/D_(ou))>2.0 or(|D_(ou)−D_(in)|/D_(in))>2.0.

How to Measure Electrical Resistance and Environmental Variation Levelof Conductive Rubber Roller:

To measure the electrical resistance of the conductive rubber roller,the conductive rubber roller was brought into pressure contact with adrum 30 mm in outer diameter made of aluminum under application of aload of 4.9 N to each of both end portions of the shaft of the roller.In the state this was rotated, a voltage of 2 kV was applied beween theshaft and the aluminum drum. Measurement was made after the conductiverubber roller was left standing for 48 hours in each environment of L/L(15° C./10% RH), N/N (23° C./55% RH) and H/H (35° C./85% RH). Thedifference between the maximum value R_(LL) of resistance value in theL/L environment and the maximum value R_(HH) of resistance value in theH/H environment measured was expressed by the difference in power [log(R_(LL)/R_(HH))]. It is preferable that the environmental variationlevel of the electrical resistance is of the power of less than 1.2.

How to Measure Non-Uniformity of Electrical Resistance of ConductiveRubber Roller:

After being left standing for 48 hours in an environment of 23° C./55%RH, the conductive rubber roller was brought into pressure contact witha drum 30 mm in outer diameter made of aluminum under application of aload of 4.9 N to each of both end portions of the shaft of the roller.In the state this was rotated, a voltage of 2 kV was applied between theconductive core material of the conductive rubber roller and the drummade of aluminum to measure the electrical resistance. The difference inresistance value between the maximum value R_(max) and minimum valueR_(min), R_(max)−R_(min), measured was expressed by the difference inpower [log(R_(max)/R_(min))]. It is preferable that the non-uniformityof electrical resistance is of the power of less than 1.2.

As shown in Table 5-1, in Examples 5-1 to 5-5, the rubber compositionfrom which the foamed rubber layer is formed is any one of i) a rubbercomposition containing 0.1 part by mass of an ethylene oxide-propyleneoxide-allyl glycidyl ether terpolymer having the propylene oxide in acompositional proportion of 1.30 mol % and the allyl glycidyl ether in acompositional proportion of 11.7 mol %, 75 parts by mass ofacrylonitrile-butadiene rubber and 24.9 parts by mass of epichlorohydrinrubber and ii) a rubber composition containing 50 parts by mass of anethylene oxide-propylene oxide-allyl glycidyl ether terpolymer havingthe propylene oxide in a compositional proportion of 1.30 mol % and theallyl glycidyl ether in a compositional proportion of 11.7 mol %, 50parts by mass of acrylonitrile-butadiene rubber and 0 part by mass ofepichlorohydrin rubber, and is irradiated with microwaves by using twoor four microwave oscillators each having an output of from 0.1 to 1.5kW, while being transported at a speed of from 0.5 to 3.0 m/min throughthe interior of a microwave vulcanizing furnace having a microwaveirradiation zone of 4 m or less. It is seen that the aspect ratios ofthe inner and outer diameters of each foamed conductive rubber form areas small as 1.06 or less and the cell diameter distribution is uniform.It is further seen that the non-uniformity of hardness of eachconductive rubber roller in the peripheral direction is small and thedesired resistance value is achieved, and that the non-uniformity ofelectrical resistance is small and the environmental variation level isof the power as small as 1.2 or less.

On the other hand, as shown in Table 5-2, in Comparative Examples 5-1 to5-5, the rubber composition from which the foamed rubber layer is formedis any one of i) a rubber composition containing 0 part by mass of anethylene oxide-propylene oxide-allyl glycidyl ether terpolymer havingthe propylene oxide in a compositional proportion of 1.30 mol % and theallyl glycidyl ether in a compositional proportion of 11.7 mol %, 70parts by mass of acrylonitrile-butadiene rubber and 30 parts by mass ofepichlorohydrin rubber and ii) a rubber composition containing 60 partsby mass of an ethylene oxide-propylene oxide-allyl glycidyl etherterpolymer having the propylene oxide in a compositional proportion of1.30 mol % and the allyl glycidyl ether in a compositional proportion of11.7 mol %, 40 parts by mass of acrylonitrile-butadiene rubber and 0parts by mass of epichlorohydrin rubber, and is irradiated withmicrowaves by using one or six, or two or four, microwave oscillator(s)each having an output of from 0.1 to 1.5 kW, while being transported ata speed of from 0.3 m/min or 3.5 m/min through the interior of amicrowave vulcanizing furnace having a microwave irradiation zone of 4 mor less. It is seen that in Comparative Example 5-4, the rubber tube isnot vulcanized and foamed and is unable to be formed as the conductiverubber roller. It is further seen that in Comparative Examples 5-1, 5-2,5-3 and 5-5, the non-uniformity of hardness, the non-uniformity ofelectrical resistance and the environmental variation level are large,and that the cell diameter distribution is poor and the aspect ratios ofthe inner and outer diameters of each foamed conductive rubber form arelarger than those in Examples. TABLE 5-1 Example 5-1 5-2 5-3 5-4 5-5EO-PO-AGE terpolymer: 0.1 50 0.1 50 0.1 Acrylonitrile-butadiene rubber:75 50 75 50 75 Epichlorohydrin rubber: 24.9 0 24.9 0 24.9 Microwaveoscillator n: (number) 2 2 2 2 4 Microwave output [1 kw × n]: (kw) 2 2 22 4 Transport speed: (m/min) 0.5 0.5 2.0 3.0 3.0 Tube aspect ratio(outer diameter): 1.02 1.06 1.02 1.04 1.01 Tube aspect ratio (innerdiameter): 1.01 1.05 1.03 1.03 1.02 Hardness non-uniformity: 1 1 1 1 0Resistance value: (Ω) 7.30E+07 1.46E+05 7.56E+07 1.35E+05 7.67E+07Electrical resistance environmental 0.98 1.12 0.97 1.11 0.95 variationlevel: (power) Electrical resistance 1.02 1.04 1.02 1.06 1.01non-uniformity: (power) Cell diameter distribution: A A A A A

TABLE 5-2 Comparative Example 5-1 5-2 5-3 5-4 5-5 EO-PO-AGE terpolymer:0 60 60 0 0 Acrylonitrile-butadiene rubber: 70 40 40 70 70Epichlorohydrin rubber: 30 0 0 30 30 Microwave oscillator n: (number) 22 4 1 6 microwave output [1 kw × n]: (kw) 2 2 4 1 6 Transport speed:(m/min) 0.3 3.5 3.5 0.3 0.3 Tube aspect ratio (outer diameter): 2.351.31 1.56 NM 1.91 Tube aspect ratio (inner diameter): 2.98 1.21 1.66 NM2.23 Hardness non-uniformity: 7 4 5 NM 7 Resistance value: (Ω) 1.21E+075.10E+06 8.20E+05 NM 9.16E+08 Electrical resistance environmental 1.871.14 1.21 NM 1.95 variation level: (power) Electrical resistance 1.381.78 2.11 NM 2.03 non-uniformity: (power) Cell diameter distribution: CB B NM CNM: not measurable

The conductive rubber roller obtained by the production process of thepresent invention and the roller for electrophotographic apparatus ofthe present invention are preferably usable as transfer rollers and soforth in image forming apparatus such as electrophotographic copyingapparatus, printers and electrostatic recording apparatus.

This application claims priorities from Japanese Patent Applications No.2005-036079 filed Feb. 14, 2005, No. 2005-036080 filed Feb. 14, 2005,No. 2005-047222 filed Feb. 23, 2005, No. 2005-049003 filed Feb. 24,2005, No. 2005-053816 filed Feb. 28, 2005, and No. 2006-027022 filedFeb. 3, 2006, which are hereby incorporated by reference herein.

1. A process for producing a conductive rubber roller having aconductive core material and a foamed rubber layer provided thereon,wherein the foamed rubber layer is formed from a rubber compositioncontaining epichlorohydrin rubber, acrylonitrile-butadiene rubber, anethylene oxide-propylene oxide-allyl glycidyl ether terpolymer, or amixture of any of these; the process has an extrusion step ofcontinuously extruding a tube composed of the rubber compositionstanding unvulcanized from a rubber extruder in a microwave vulcanizingunit, and a forming step of foaming and vulcanizing said tube by meansof a microwave irradiator having a microwave irradiation zone of 4 m orless in length while being transported at a speed of from 0.5 to 3.0m/min to form a foamed rubber tube; and the foamed rubber tube has aninner diameter smaller by from 20 to 35% than the outer diameter of saidconductive core material over a whole region in the lengthwise directionof the conductive rubber roller, and the conductive core material ispress-fitted into the foamed rubber tube without using any adhesive. 2.The process for producing a conductive rubber roller according to claim1, which further includes a step of heating and vulcanizing the foamedrubber tube having passed through the microwave irradiator at atemperature of from 150 to 300° C. for from 2 to 10 minutes by using ahot-air heating means having a gas furnace as a heat source.
 3. Theprocess for producing a conductive rubber roller according to claim 1,wherein the forming step of foaming and vulcanizing said tube is carriedout by using two or four microwave oscillators having an output of from0.1 to 1.5 kW per oscillator, to effect irradiation at a totalirradiation output of from 0.3 to 3.0 kW of the microwave irradiator. 4.The process for producing a conductive rubber roller according to claim1, wherein the rubber composition contains azodicarbonamide.
 5. A rollerfor electrophotographic apparatus, wherein the conductive rubber rollerproduced by the process for producing a conductive rubber rolleraccording to claim 1 is used as a base layer member.
 6. The roller forelectrophotographic apparatus according to claim 5, wherein said rolleris a transfer roller.
 7. A process for producing a conductive rubberroller having a conductive core material and a rubber layer providedthereon, wherein the rubber layer contains at least acrylonitrilerubber, epichlorohydrin rubber and a blowing agent, the rubber layer hasa gas generation rate of from 2 ml/g·min to 4 ml/g·min at 170° C. to230° C., and the process has a vulcanizing and foaming step ofvulcanizing and foaming the rubber layer by using a microwavevulcanizing furnace which provides hot air and irradiation withmicrowaves, where temperature of heating atmosphere in the microwavevulcanizing furnace in the vulcanizing and foaming step is so controlledthat a ratio of initial vulcanizing time T10 to initial foaming timeTp10, T10/Tp10, of the rubber layer is from 1 or more to less than 3 andthe T10 is within 90 second.
 8. The process for producing a conductiverubber roller according to claim 7, wherein the rubber layer contains athiuram type accelerator and a thiazole type accelerator, and thethiuram type accelerator has a molecular weight of from 200 or more to650 or less.
 9. A conductive rubber roller comprising a conductive corematerial and a rubber layer provided thereon, used in anelectrophotographic apparatus, and having been produced by the processfor producing a conductive rubber roller according to claim 7, whereindiameters of foam cells in said conductive rubber roller are 0.3 mm orless.
 10. Use of the conductive rubber roller according to claim 9 as atransfer roller in an image forming apparatus having anelectrophotographic photosensitive member, a charging means, an exposuremeans, a developing means and a transfer means; said transfer rollerbeing set in said transfer means.
 11. A conductive rubber roller havinga conductive core material and a rubber layer provided thereon, whereinsaid rubber layer contains at least acrylonitrile rubber,epichlorohydrin rubber and carbon black, the carbon black being in acontent of from 5 to 30 parts by mass based on 100 parts by mass of thetotal of the rubbers, said rubber layer has a dielectric losscoefficient εr·tan δ of from 0.3 to 0.5 in an unvulcanized state, andsaid rubber layer has been vulcanized and foamed by means of a microwavevulcanizing furnace which generates hot air and microwaves of 2,450±50MHz.
 12. A process for producing a conductive rubber roller having aconductive core material and a rubber layer provided thereon, whereinsaid rubber layer contains at least acrylonitrile rubber,epichlorohydrin rubber and carbon black, and the process has a kneadingsteps of kneading the acrylonitrile rubber, the epichlorohydrin rubberand the carbon black in such a manner that the carbon black is in acontent of from 5 to 30 parts by mass based on 100 parts by mass of thetotal of the rubbers, and a step of vulcanizing and foaming the rubberlayer by means of a microwave vulcanizing furnace which generates hotair and microwaves of 2,450±50 MHz, where a dielectric loss coefficientεr·tan δ of unvulcanized rubber through the kneading step is from 0.3 to0.5.
 13. Use of the conductive rubber roller according to claim 11 as atransfer roller in an image forming apparatus having anelectrophotographic photosensitive member, a charging means, an exposuremeans, a developing means and a transfer means; said transfer rollerbeing set in said transfer means.
 14. A process for producing aconductive rubber roller having a conductive core material and a foamedrubber layer provided thereon, wherein said foamed rubber layer isformed through a step of carrying out vulcanization and foaming byirradiation with microwaves and hot air in a microwave vulcanizingfurnace, the microwave vulcanizing furnace has a transport means whichis a mesh belt coated with polytetrafluoroethylene, and, a ratio of anouter diameter A (mm) of the rubber layer after vulcanization to a meshopening percentage B (%) of the mesh belt, A/B, is from 0.2 or more to0.4 or less.
 15. A conductive rubber roller used in anelectrophotographic apparatus, which has been produced by the processfor producing a conductive rubber roller according to claim 14, and hasa difference in Asker-C hardness of 1° or less in the peripheraldirection.
 16. Use of the conductive rubber roller according to claim 15as a transfer roller set in a transfer assembly of anelectrophotographic apparatus.
 17. A process for producing a conductiverubber roller having a conductive core material and a foamed rubberlayer provided thereon, wherein a rubber composition which forms saidfoamed rubber layer contains 0.1 to 50.0 parts by mass, based on 100parts by mass of total polymer content, of an ethylene oxide-propyleneoxide-allyl glycidyl ether terpolymer having the propylene oxide in acompositional proportion of from 1 to 20 mol % and the allyl glycidylether in a compositional proportion of from 5 to 15 mol %, and theprocess has an extrusion step of continuously extruding a tube composedof the rubber composition standing unvulcanized from a rubber extruderin a microwave vulcanizing unit having an output of from 0.1 to 1.5 kW,and a forming step of foaming and vulcanizing said tube by means of amicrowave irradiator having a microwave irradiation zone of 4 m or lessin length while being transported at a speed of from 0.5 to 3.0 m/min toform a foamed rubber tube.
 18. The process for producing a conductiverubber roller according to claim 17, which further includes a step ofcontinuously vulcanizing the foamed rubber tube having passed throughthe microwave irradiator by a hot-air heating means having a gas furnaceas a heat source.
 19. The process for producing a conductive rubberroller according to claim 17, wherein the forming step of foaming andvulcanizing said tube is carried out by means of a microwave irradiatorusing two or four microwave oscillators having an output of from 0.1 to1.5 kW per oscillator.
 20. The process for producing a conductive rubberroller according to claim 17, wherein the rubber composition containsazodicarbonamide.
 21. A conductive rubber which has been produced by theprocess for producing a conductive rubber roller according to claim 17,and has a resistivity of from 1×10⁵ to 5×10⁸Ω in an environment of 23°C. and 55% RH.
 22. A roller for electrophotographic apparatus, whichuses as a base layer member the conductive rubber roller produced by theprocess for producing a conductive rubber roller according to claim 17.23. Use of the roller for electrophotographic apparatus according toclaim 22 as a transfer roller set in a transfer assembly of anelectrophotographic apparatus.